1. Field of the Invention
This invention relates to medical instruments. It applies specifically to disposable hypodermic needles and in the U.S. Patent Office it would be found in a classification for needle tip guards which protect health care workers from accidental needle sticks.
2. Description of the Prior Art
The need for protection of health care workers from infectious diseases such as hepatitis and AIDS due to accidental needle sticks by now has been well documented. A preponderance of devices have evolved for single use hypodermic needles which either provide a protective cover for the needle tip after usage or withdraw the needle back up inside the syringe. Unfortunately the vast majority of these devices have inherent drawbacks which render them unsuitable as practical products. Most are unduly complex, bulky, cumbersome and quite costly in relation to the low cost of manufacture for simple needles and their attached hubs. Perhaps the most common disadvantage of almost all existing guards and protection systems is that they require something additional from the user beyond what is required for normal operation.
The ideal guard should be simple and yet positively locking in both directions such that it prevents the needle tip from escaping while keeping itself locked onto the needle. It should be very low cost which means using little material, using the very bare minimum of preferably standard parts, and configuring the guard for use with standard hypodermic needles. That is, the guard should not require that the needle be modified for proper operation. Since needles are usually made by totally automated machines, the cost of needle modification could make such a guard cost prohibitive. Also, the ideal guard should be entirely automatic. Any needle which requires additional effort or operational steps to use would be resisted by the medical community, and any needle guard which must be manually activated stands a good chance in many situations of not being used at all. This would be especially true in emergency situations where the possibility of accidents is already higher anyway.
Some of the devices of the prior art such as an invention by Vaillancourt (U.S. Pat. No. 4,804,371) issued in 1989 can be examined in light of the desirable characteristics of an ideal guard. One embodiment of the Vaillancourt guard shows a cap extended over the needle tip by a spring. The cap does not positively lock and the mechanism must be manually activated after the needle is used. Another embodiment, an accordian-like sheath, must be manually extended and is relatively bulky.
A later device by Martin et al. (U.S. Pat. No. 4,887,998) provides a partial sleeve on a spring and an occluding ball trap which prevents the tip from exiting but does not prevent motion in the other direction and thus the guard does not positively lock. This mechanism must also be manually activated and is unduly complex and costly.
Inventions of Sudnak (U.S. Pat. No. 4,894,055) and Paris (U.S. Pat. No. 4,911,693) both provide spring loaded total sleeves which entirely enclose the needle. They are bulky, costly and must be manually activated.
The other family of protective devices provide for retraction of the needle up into the syringe body or an extension of the syringe after usage. These devices require highly modified syringes or highly modified syringe/needle combinations and are quite complicated and therefore costly. Attempts have been made to minimize the extra motion or effort required to activate these devices. The Vadher needle (U.S. Pat. No. 4,946,446) retracts when the syringe plunger is pushed once again after use, so activation is still not entirely automatic and may not occur at all if the operator is unfamiliar with the particular mechanism or is in a hurry.
The Lennox needle (U.S. Pat. No. 4,966,593) retracts when the plunger is pushed all the way down. This makes the device impractical for using the plunger to fill the syringe (such as in drawing blood or drawing medication from another container) and still does not guarantee that the mechanism will be activated.
Unique to the guards in this survey of the prior art is a device of this inventor (McLees, U.S. Pat. No. 5,059,180) which issued in 1991. It consists of a spring and a small bead-like guard which resides initially near the needle tip and which becomes activated when the skin pushes the guard back from the tip at insertion. Thus it is the act of insertion which activates the guard and normal usage of the needle guarantees that activation must automatically occur. The guard is also simple, low cost and positively locking. However, it requires a special needle with a raised shoulder. From the standpoint of potential manufacturers this fact makes the needle cost prohibitive. Obviously it would be desirable to have a guard similar in concept which can be used with a standard needle.